1. Field of the Invention
This invention relates to abrasive cutting blades having a polycrystalline structural ceramic core, which are useful in the cutting or dicing of silicon wafers and other hard, and/or brittle materials. The cutting discs of this invention are particularly useful in the die-separation phase of the production of semi-conductor chips, magnetic heads and other components for use in the electronics industry.
2. Description of the Prior Art
In the die-separation or dicing stage of the production of microelectronic devices, silicon, ceramic or other exotic hard and brittle substances are sliced using an abrasive machining process analogous to other grinding and cut-off operations. The comparatively high cost of these substrates and the need for high accuracy in dicing makes it essential that the cutting blades be highly accurate so as to minimize waste of material and to minimize secondary finishing operations. The circular cutting blades also should be as thin as possible so that the kerf (width of the cut) is as thin as possible.
The blade used in the cutting process contains a large number of small, abrasive grains on the cutting surface. Typically, the abrasive grains are diamond particles, although other hard, natural and synthetic particulate materials may be used. The blades operate at high rpm, typically up to 50,000 rpm. To obtain trueness of cut and stability, and to minimize run-out (movement of the cutting edge out of the desired plane), the blades are typically mounted in a flange so that only a small cutting edge is exposed. The depth of cut using such a device is limited by the flexibility of the blade.
There are three basic types of dicing blades which are commericially available. The sintered blade has abrasive particles fused into a soft metal, such as brass or copper, or incorporated using a powdered metallurgical process. The plated diamond blade holds abrasive particles in a nickel bond produced by an electroplating process. The resinoid blade contains the abrasive particles in a homogeneous matrix of a resin, typically a thermosetting resin.
The core of the blade may be made of resin or metal or it may be made of a vitrified ceramic. U.S. Pat. No. 4,099,934 to Suzuki et al discloses a method for resin bonding an abrasive to a metal base. U.S. Pat. No. 4,385,907 to Tomita et al . discloses a resinoid bonded grinding wheel in which the support member is a vitrified ceramic. U.S. Pat. No. 4,446,657 to Asaeda et al discloses a method for resin bonding an abrasive to a porous, vitrified ceramic grinding wheel.
Vitrified clay-based, porous ceramic blade cores are more heat stable than metal blade cores but the width of the blade cannot be made as narrow as desired for minimal kerf without producing a blade which is too fragile. Also, it has been found that when the exposure of the cutting edge of the blade is increased to that necessary to cut through thicker materials, contact of the vitrified ceramic core of the blade with the substrate being cut results in catastrophic destruction of the blade.